Check to see how redundancy is set ,if its RPR mode then it will take considreably longer than SSO mode . Either the config was never set as SSO or you have mismatched IOS versions in the supervisors which will only run in RPR if the versions do not match . If in RPR mode all ports will reset which causes spanning tree and other functions to runn which is probably what you saw and the corrresponding interuption . SSO is the way to go !!!